1. Field of the Invention
The present invention relates to a production system and a production method for a product in which a work in process undergoes processing in multiple steps to be completed as a product. More particularly, the present invention relates to a production system and a production method for a composite product such as an electronic appliance in which element groups each constituted by a plurality of members are combined.
2. Description of the Related Art
A product constituted by a semiconductor integrated circuit such as a well-known very-large-scale integrated circuit (VLSI) is completed as a result of multiple steps. As a system for producing such a product, a production system called a job shop system is used in which manufacturing apparatuses of one kind are arranged in one place in a factory and other apparatuses are arranged in the same manner to form facility groups, and a work in process is moved from one facility group to another to be finished as a product. This production system has such characteristics as to enable simultaneous production of a number of different kinds of product and changing of kinds of product and to frequently change the manufacturing process for the purpose of improving yields, stabilizing qualities and improving functions.
A semiconductor integrated circuit is manufactured by performing photolithographic processes in combination with forming of an oxide film or a nitride film, ion implantation and heat treatment, deposition of a metal or semiconductor film, forming of an interlayer insulating film, etc. Several hundred process steps for such processings are required for manufacturing of a VLSI. The term “Design rules” is a generic name for manufacturing process techniques relating to a minimum processing dimension. Ordinarily, design rules specify the gate length or channel length of transistors. A smaller design rule value signifies finer processing. For example, for 64-Mbit dynamic random access memory (DRAM), a process with 0.25 to 0.18 μm is used.
A production line is constituted by a film forming apparatus for forming a coating film, an etching apparatus for etching the film, an exposure apparatus for forming a mask pattern by using a photomask, an annealing apparatus for heat treatment, an industrial robot for conveying substrates, etc. In any production line, a semiconductor is treated with great care so as not to be contaminated by physical contamination with dust or the like, chemical contamination with phosphorous, boron, an organic material gas or the like, or chemical contamination with a metal or alkali metal, such as iron, nickel or sodium, in order to ensure fine accurate processing, high reproducibility and stability of quality. The product line is therefore constructed in a special environment provided in a factory and called a clean room.
To complete a product, multiple steps are executed in predetermined order. Processing in each step proceeds as batch processing or single-wafer processing of a plurality of substrates set as one unit. This unit is called a lot and is treated as a unit in physical distribution in the production system.
As products constituted by a semiconductor device, liquid crystal display devices constructed by forming semiconductor integrated circuits directly on a substrate such as glass, electroluminescent (EL) panels, EL modules, etc., are known as well as memories and microprocessors constructed by forming metal-oxide-semiconductor (MOS) transistors on a semiconductor substrate. Elements forming integrated circuits in liquid crystal display devices use a semiconductor thin film and are therefore called “thin-film transistor (TFT)”. A liquid crystal display device is a composite type of product in which a group of elements constituted by TFTs (called a TFT array) and liquid crystal elements each formed in such a structure that a liquid crystal is interposed between a pair of electrodes are combined and the switching characteristic of the TFTs and the electrooptical effect of the liquid crystal are utilized. An EL panel is a composite type of product in which a group of elements constituted by TFTs and EL elements in which an organic compound provided as a light-emitting member is interposed between a pair of electrodes are combined and the switching characteristic of the TFTs and the electroluminescent phenomenon of the EL material are used in combination. An EL module is a composite type of product in which an external circuit such as a controller is added to an EL panel. Each of these products has active elements, i.e., TFTs, arranged in vertical and horizontal directions in matrix form and displays images by using the thus-arranged elements, and is therefore called an active matrix type.
TFTs are produced by semiconductor integrated circuit techniques similar to those for producing VLSI. There is only a small difference therebetween, which is a step of forming a semiconductor film on an insulating surface. It can be said that processing is performed almost in the same manner in other steps, i.e., a gate forming step, an impurity element implantation step, a wiring forming step, etc. An inspection step is incorporated in a TFT process if necessary. The production yield is controlled on the basis of inspection information obtained in the inspection step. The design rules for the above-described display devices use a large minimum dimension of several microns. However, the contamination level allowable in a process for manufacturing the above-described display devices is said to be the same as that in a process for manufacturing the 64-Mbit DRAM.
With composite products each having semiconductor elements and a liquid crystal elements or a light-emitting element constituted by members different in a physical property, which are strictly controlled in a production line, there is a problem in that there is a possibility of one of the two different kinds of element being contaminated by the constituent members of the other to cause a defect. As a specific example, an alkali metal or an alkali earth metal is used in a cathode material in a light-emitting element. If this element contaminates semiconductors, a malfunction of the product may be caused. This contamination not only occurs in the composite product package integrally formed but also appears in an environment surrounding the fabrication line as a secondary contamination to affect the process of producing the product.
As a production means for improving the production efficiency, a method is used in which the size of a substrate on which element groups are formed is increased to enable a larger number of members to be obtained from one substrate. If the size of a substrate is increased, the manufacturing apparatus and the line constituting the manufacturing apparatus are increased. However, if the processing time per substrate is not largely changed, the production capacity is increased. However, the method of increasing the substrate size cannot be simply used for reasons relating to the construction of the apparatus with respect to processings such as coating film formation and etching.
With the increase in variety of products required on the market, a need has arisen to form a production system with flexibility to meet a demand for wide-variety small-lot production. However, conventional lot-by-lot production systems cannot always be formed with flexibility to meet such a demand. With conventional lot-by-lot production systems, there is a problem in that if the size of a substrate is increased to increase the number of members taken from the substrate, an excessively large number of products are produced or the number of substrates in one lot is reduced and production cannot be performed with efficiency.
It is important to acquire increased market share and to maintain its advantage on the market by advancing the development of techniques in forefront of technology for producing as information devices composite products using a combination of semiconductor elements and a liquid crystal element or a combination of semiconductor elements and a light-emitting element, and by manufacturing and selling products protected by intellectual property rights ahead of all competitors. However, an enormous capital and payload are required for manufacturing and selling a completed product involving designing of composite products, designing of processes, designing and optimization of manufacturing apparatuses, optimization of manufacturing conditions, accumulation of know-how, etc., and, on the other hand, there is a risk of getting behind some other company in technological development. The risk is doubled in the electronic device market where commodities are changed in short cycles. A combination of an element substrate on which a semiconductor element is formed and a liquid crystal element or a combination of semiconductor elements and a light-emitting element apparently seems to be simple. However, the circuit configurations, the drive methods, the drive conditions, etc., therefor differ from each other, and the optimum element structures in the semiconductor elements are not the same.